This invention is related to valve seat assemblies having a seat ring which incorporates a resilient deformable sealing member around a peripheral portion thereof to function as a seal between the seat member and the adjacent valve body, and as a spring to urge the seat ring into contact with the valve member. More particularly this invention is related to a seat assembly for a parallel sided gate valve member. The seat assembly uses an annular resilient member positioned around the perimeter of the seat member to seal around the seat member and at the same time be compressed to urge the seat member or ring toward the gate member.
Several valve seat assemblies are known in the art which utilize an annular resilient sealing member around the periphery of a seat ring to function as a seal and as a spring to urge the seat member toward the valve member. However, these constructions are limited to resilient members mounted at the outer extremity of the seat member or in the outer rectangular corner portion of the seat pocket as formed by the seat recess side wall and end wall. Constructions of this type in which the resilient member functions both as a spring and a seal are shown in the U.S. Pat. Nos. to R. M. Estes, et al. 3,078,865, to C. E. Anderson, et al. 2,985,421, and to L. F. Eckerd, Jr. 3,006,599. In these referenced prior art devices the resilient member is positioned on the outer peripheral portion of the seat members in a chamber formed by a peripheral groove in the outer end of the seat member and a corner of the bottom portion of the body recess. In order for these seat constructions to function adequately they must be constructed with considerable control of their dimensions. Dimensional tolerances of the recess, the seat member, and the resilient member must be quite small for the constructions to function properly. In order that these prior art seat constructions function properly the tolerances of the parts concerned as well as the dimension of the gate member between opposed sealing surfaces thereof must be maintained within quite small ranges to insure sealing and to prevent compression of the resilient member beyond its elastic limit. In general, tolerances of the known prior art devices must be very closely controlled and this is an expensive and very time consuming procedure for a manufacturer because of the precise control necessary in all steps of the machining of such parts in addition to the quantity of parts which must be scrapped and reworked because their tolerances fall outside of the allowable range. Also, displacement of the seat members is typically quite small to prevent excessive compression of the resilient member and to lessen the resilient spring effect of compressing a resilient member.
Another disadvantage of the prior art valve seat constructions is that the resilient sealing members must be sized such that they can be retained over the perimeter of the seat member as the seat member is inserted into the recess and this requires a greater force to displace the resilient member radially outward for sealing against the recess annular wall.